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Full text of "Proper locations for storage precipitation gages"

BLM LIBRARY 




T/N 257 

Filing Code 7200 

Date Issued January 1975 



TECHNICAL NOTE 



U.S. DEPARTMENT OF THE INTERIOR - BUREAU OF LAND MANAGEMENT 



PROPER LOCATIONS FOR 
STORAGE PRECIPITATION GAGES 



By 

David W. Moore 

Vernal District, Utah 





Additional copies of Technical Notes are available from DSC, Federal Center Building 50, Denver, Colo., 80225 



.. 

The proper location of precipitation gages will improve the reliability 
of rainfall records and management decisions. 



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Most BLM districts maintain a network of storage precipitation gages. 

Many of these have been in operation for 15 or more years. If the gages 

were not properly placed when installed, records can be in error as 
much as 25 per cent. 

To improve the reliability of precipitation information, gage locations 
should be reviewed for adequate placement. If found to be in poor 
locations, gages should be moved to better sites. However, when a gage 
is relocated, its past record should be retained for possible future 
adjustment based on data at the new location. 

The following guidelines can be used to improve the accuracy of precip- 
itation records: 

1. Avoid bare ridges and benches. (Figure 1) 

2. Where possible, use Pinyon Juniper, large shrubs, or 
similar vegetation as a wind shield. This can be done 
by using the following rules: 

Starting at the top of the container, measure up and 
out at a 45° angle. All vegetation should fall out- 
side the imaginary cone. (Figure 2) 
A better rule, when possible, is to be sure that the 
distance from the shielding vegetation to the gage is 
equal to at least twice the height of the vegetation. 
(Figure 2a) 

3. When a gage must be placed in an area of tall trees 

(> 50 feet), a clearing should be used that has a minimum 
diameter of 50 feet. (Figure 3) 

4. Small canyons and draws are better than no protection 
at all, but should be avoided if possible. (Figure 4) 

5. If none of the above is available, a commercial wind 
shield should be considered for the gage. (Figure 5) 

If the above suggestions are followed, precipitation information will 
be accurate and of greater value in BLM management decisions. 



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Figure 1. Avoid unprotected areas, 



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Figure 2. The cone above the gage should not be obstructed. 




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Figure 2a. When possible, the distance between gage and shielding 
vegetation should be twice the height of the vegetation. 



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Figure 3. The opening in the trees should be at least 50 feet wide. 




Figure 4. Even a little protection helps. 




Figure 5. A commercially built wind shield can take the place of natural 
protection. 



GPO 857 - 962 



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